Process for the production of surface-treated carbon black for the reinforcement of rubbers

ABSTRACT

A process for producing surface-treated carbon black for rubber reinforcement characterized by providing carbon black and organosiloxane together; and then heating the mixture to a temperature of 60° C. to 200° C. to deposit a silicon dioxide residue on the surface of the carbon black and a rubber composition using the same.

TECHNICAL FIELD

The present invention relates to a process for producing carbon blacktreated on the surface thereof with silica. More specifically, itrelates to carbon black for tires and other various types of rubberproducts having the superior tan δ temperature dependence possessed bysilica and improved wear resistance and electrical conductivity and to arubber composition containing the same.

BACKGROUND ART

Reinforcing fillers such as carbon black, silica have beenconventionally used for reinforcing rubber. Silica, as compared withcarbon black, has properties of a low tan δ at high temperatures (aroundto 60° C.) and a high tan δ at low temperatures (around to 0° C.), andtherefore, when used for rubber compositions for tire treads, a tirehaving a low rolling resistance and a high gripping power can beadvantageous produced. However, silica, is inferior to carbon black inwear resistance and has a low electrical conductivity, and therefore, ifsilica is used for tires, there is the problem that the tire will pickup a charge when driven on and will cause various problems. These andother problems have not been solved yet.

On the other hand, it has been proposed in, for if example JapaneseExamined Patent Publication (Kokoku) No. 50-14254 and Japanese ExaminedPatent Publication (Kokoku) No. 7-30269 that, by coating the surface ofa pigment etc. with, for example, silica the surface charge thereof ischanged whereby the dispersibility is improved and the weatherresistance is increased. For example, Japanese Examined PatentPublication (Kokoku) No. 7-30269 discloses a method for treating thesurface of carbon black for a powder coating composition comprised ofdispersing carbon black in water, adjusting the pH thereof to 6 or more,and, while maintaining the temperature of 70° C. or more, using sodiumsilicate to cause amorphous silica to precipitate on the surface of theparticles of carbon black. However none of these publications disclosesthe deposition of silica on the surface of the carbon black forreinforcing the rubber.

Further, various patents disclose the treatment of carbon black withsilicon compounds.

For example, Japanese Unexamined Patent Publication (Kokai) No.53-100190, Japanese Unexamined Patent Publication (Kokai) No. 56-38357,and Japanese Unexamined Patent Publication (Kokai) No. 61-291659disclose the mixing and drying of a silicone compound and carbon black.

However, these prior arts do not refer to the superior properties inapplications for reinforcement of rubber obtained by the formation ofthe composites of carbon black and silica.

Further, Japanese Unexamined Patent Publication (Kokai) No. 58-125249discloses the mixing of carbon black coated with a silane coupling agenton the surface thereof to a thermoplastic resin, but this publicationalso does not describe anything regarding the superior properties whenblending with rubber, in the same way as the above.

Japanese Unexamined Patent Publication (Kokai) No. 4-233976 discloses aprocess for producing a heated reaction product of a silicon compoundhaving two or less silicone atoms in a molecule with carbon black as acarbon black chemically modified with an organosilicon compound and arubber composition including the same. This is intended to provide, atthe surface of the carbon black, various organic groups throughalkoxysilyl groups. The deposition of silica on the surface of thecarbon as in the present invention is a fundamentally differenttechnical idea.

DISCLOSURE OF INVENTION

Accordingly, objects of the present invention are to provide a processfor producing surface-treated carbon black suitable for reinforcement ofa rubber having the superior tan δ temperature dependence possessed bysilica and having an excellent wear resistance and electricalconductivity and to provide a rubber composition including the same.

In accordance with the present invention, there is provided a processfor producing surface-treated carbon black comprising providing thepresence of carbon black and organosiloxane together, then heating thecarbon black and the organosiloxane to less than the temperature atwhich the carbon black is oxidized and to more than the temperature atwhich the organosiloxane is decomposed or adhered, whereby silicondioxide residues is deposited on the surface of the carbon black.

BEST MODE FOR CARRYING OUT THE INVENTION

The inventors engaged in intensive studies on a process for productionof surface-treated carbon black suitable for use in rubber reinforcementwhich, as explained above, provides a rubber having the superior tan δtemperature dependency possessed by silica, and having excellent wearresistance, and having no problems derived from a low electricalconductivity. As a result, we discovered that it was possible to producethe desired carbon black by heating carbon black and organosiloxane,together, at a temperature of less than the temperature at which thesurface of the carbon black is oxidized (normally less than about 200°C.) and at a temperature of more than the temperature at which theorganosiloxane is decomposed or condensed (generally about 60° C. ormore), whereby silicon dioxide (SiO₂) residues is deposited or adheredon the surface of the carbon black.

The organosiloxane usable as the starting material in the presentinvention is known in the art. For example, those having the followingstructure are exemplified. ##STR1## wherein, R₁, R₂, R₃, and R₄ are atleast one organic group selected from the group consisting ofconventionally known organic groups and may be the same or may be alldifferent. Examples of such an organic group are C₁ to C₄ alkyl groups,C₁ to C₄ alkoxy groups, and also alkylamino groups (e.g., --RNH₂,--RNHR'NH₂, --RNH₂), epoxy groups (e.g., ##STR2## carboxyl groups (e.g.,--RCOOH) carbinol groups (e.g., --R' CH), methacrylic acid groups (e.g.,--RC (CH₃)═CH₂), mercapto groups (e.g., --RSH), alkylphenyl groups(e.g., ##STR3##

Particularly preferable organosiloxanes are those having in the moleculethereof an alkoxysilyl group-SiOR, wherein R is an alkyl group having 1to 4 carbon atoms, with each molecule containing at least 3 and not morethan 1000, preferably at least 7, more preferably at least 10, siliconatoms. If the number of the silicon atoms is small, the contact thereofwith the carbon black and bonding efficiency becomes unpreferably poor.Conversely, if the number of the silicon atom is more than 1000, theviscosity becomes higher, and therefore, the processing becomesdifficult. The amount of the organosiloxane added is not particularlylimited, but an amount of 0.1 to 50% by weight, in terms of SiO₂, basedupon the weight of the carbon black is preferable and 0.5 to 30% byweight is more preferable. If the amount used is too small, naturallythe desired effects cannot be obtained, while conversely if too large,the electroconductivity is unpreferably decreased.

As the carbon black usable as the starting material in the presentinvention, it is possible to use any carbon black which isconventionally used in the past for tires and other rubber compositions.Preferable carbon blacks are SRF to SAF grades. It is possible to usethe same in various manners or by blending two or more types thereof,depending upon the application of the rubber composition.

A general method for producing the surface-treated carbon blackaccording to the present invention will be explained below.

First, a predetermined amount of the carbon black preferablyungranulated, is measured, followed by adding organosiloxane in anamount corresponding to 0.5 to 50% by weight, in terms of the amount ofsilica. The mixture is agitated and mixed at an ordinary temperaturewith a closed type powder mixer, for example, a universal mixer made byDalton Co. The organosiloxane may be added, after diluting with asuitable solvent in order to facilitate the dispersing thereof. Themixture of organosiloxane and carbon black mixture thus sufficientlyagitated is then heated on, for example, a hot plate at a temperaturerange of 60° C. to 200° C.

The silica surface-treated carbon black for reinforcing rubber accordingto the present invention can be compounded to any cross-linkable rubbercomponent to obtain a rubber composition having superior wearresistance, grip performance, rolling resistance, etc. Examples of sucha cross-linkable rubber are natural rubber (NR), various types ofbutadiene rubbers (BR), various types of styrene-butadiene copolymers(SBR), polyisoprene rubbers (IR), butyl rubbers (IIR), halogenated butylrubbers, acrylonitrile-butadiene rubbers, chloroprene rubbers,ethylene-propylene copolymer rubbers, ethylene-propylene-diene copolymerrubbers, styrene-isoprene copolymer rubbers, styrene-isoprene-butadienecopolymer rubbers, isoprene-butadiene copolymer rubbers,chlorosulfonated polyethylene, acryl rubbers, epichlorohydrin rubbers,polysulfide rubbers, silicone rubbers, fluororubbers, urethane rubbers,etc. These may be used alone or in any blend thereof. When using ablend, the ratio of the blend is not particularly limited.

The silica surface-treated carbon black according to the presentinvention is preferably blended in an amount of 10 to 200 parts byweight of the silica surface-treated carbon black, based upon 100 partsby weight of the rubber component, more preferably 15 to 150 parts byweight. If the amount blended is too small, the rubber cannot besufficiently reinforced, and therefore, the wear resistance etc.deteriorates. Conversely, if the amount blended is too large, there isthe danger of, for example, the hardness becoming too high, and theprocessability falling, whereby the practical usefulness as a rubbermaterial becomes poor. It is also possible to use in the rubbercomposition any carbon black and/or silica normally compounded intorubber compositions, in addition to the above surface-treated carbonblack.

The above-mentioned rubber composition may also optionally contain, inaddition to the above rubber, the carbon black having the silicadeposited on the surface thereof, etc., any compounding agent, normallyused in the rubber industry, such as sulfur, organic peroxides,softening agents, antioxidants, vulcanization accelerators, fillers,plasticizers, silane coupling agents, etc. in an amount conventionallyused.

EXAMPLES

The present invention will now be explained below in further detail withreference to Examples, but it should be noted that the present inventionis, of course, not restricted to these examples in scope. Note that themethods of evaluation used in the Examples are as follows:

Methods for Measurement of Properties of Surface-Treated Carbon Black

1) Silica Content

A sample of the surface-treated carbon black was calcified in anelectric furnace at 600° C., the ash was subjected to a fluorinationtreatment, and the reduction in weight was treated as the silicacontent. This was shown as a percentage by weight based upon theoriginal surface-treated carbon.

2) Nitrogen Specific Area

This was measured according to a method of ASTM D3037.

Methods for Measurement of Physical Properties of Rubber

tan δ

This was measured for a sample piece having a width of 5 mm using aviscoelasticity spectrometer made by Toyo Seiki Seisakusho under anamplitude of ±2%, a frequency of 20 Hz, and a static stress of 10%.

REFERENCE EXAMPLES 1 AND 2

Surface-Treated Blacks 1 and 2 according to the present invention wereprepared as follows:

Surface-Treated Black 1

100 g of methylethoxy siloxane having a polymerization degree of 40 wasadded as an organosiloxane to 1 kg of carbon black N339 (Diablack N339ungranulated, made by Mitsubishi Chemicals), followed by mixing in auniversal mixer made by Dalton Co. at ordinary temperature for about 10minutes. Next, the mixture was uniformly and thinly spread over a hotplate at 180° C. and heat treated for about 6 hours. The surface-treatedblack obtained after the heating was calcified and the amount of SiO₂measured by the above method was found to be 5.3% by weight.

Surface-Treated Black 2

60 g of silanol-terminal dimethylpolysiloxane (L-9000 (8000): made byNippon Unicar K.K.) was added as an organosiloxane to 1 kg of carbonblack N339 (Diablack N339 ungranulated, made by Mitsubishi Chemicals),followed by treating in the same way as Surface-Treated Black 1 toobtain the surface-treated black. The amount of SiO of thesurface-treated black was 3.3% by weight.

EXAMPLES 1 to 4 AND COMPARATIVE EXAMPLES 1 to 4

The components, other than the vulcanization system, in the formulationshown in Table 1 were mixed in an 1.8 liter closed type mixer for 3 to 5minutes. When reaching the temperature to 165±5° C., the mixture wasdischarged to obtain a master batch. The master batch was then mixedwith the vulcanization accelerator and sulfur with an 8-inch open rollto obtain a rubber composition. The rubber composition obtained wasmeasured for the unvulcanized processability. Next, the composition waspress vulcanized in a 15×15×0.2 cm mold at 160° C. for 20 minutes toprepare the desired test piece (rubber sheet), which was then evaluatedas to the vulcanized physical properties by the above methods. Theresults are shown in Table I.

                                      TABLE I                                     __________________________________________________________________________             Comparative Example                                                                           Example                                                       1   2   3   4   1   2   3   4                                        __________________________________________________________________________    SBR1502*.sup.1                                                                         100.00                                                                            100.00                                                                            100.00                                                                            100.00                                                                            100.00                                                                            100.00                                                                            100.00                                                                            100.00                                   Silica*.sup.2                                                                          40.00                                                                             --  60.00                                                                             --  --  --  --  --                                       N339*.sup.3                                                                            --  40.00                                                                             --  60.00                                                                             --  --  --  --                                       Surface treated                                                                        --  --  --  --  40.00                                                                             --  60.00                                                                             --                                       black 1*.sup.4                                                                Surface treated                                                                        --  --  --  --  --  40.00                                                                             --  60.00                                    black 2*.sup.4                                                                S169*.sup.5                                                                            4.00                                                                              --  6.00                                                                              --  2.00                                                                              2.00                                                                              3.00                                                                              3.00                                     Diethylene                                                                             2.00                                                                              --  3.00                                                                              --  --  --  --  --                                       glycol*.sup.6                                                                 ZnO      3.00                                                                              3.00                                                                              3.00                                                                              3.00                                                                              3.00                                                                              3.00                                                                              3.00                                                                              3.00                                     Stearic acid                                                                           2.00                                                                              2.00                                                                              2.00                                                                              2.00                                                                              2.00                                                                              2.00                                                                              2.00                                                                              2.00                                     Antioxidant*.sup.7                                                                     2.00                                                                              2.00                                                                              2.00                                                                              2.00                                                                              2.00                                                                              2.00                                                                              2.00                                                                              2.00                                     Sulfur   2.00                                                                              2.00                                                                              2.00                                                                              2.00                                                                              2.00                                                                              2.00                                                                              2.00                                                                              2.00                                     Accelerator PG*.sup.8                                                                  1.00                                                                              --  1.00                                                                              --  --  --  --  --                                       Accelerator NS*.sup.9                                                                  0.50                                                                              1.00                                                                              0.50                                                                              1.00                                                                              1.00                                                                              1.00                                                                              1.00                                                                              1.00                                     Total (PHR)                                                                            156.50                                                                            150.00                                                                            179.50                                                                            170.00                                                                            152.00                                                                            152.00                                                                            173.00                                                                            173.00                                   tanδ (0° C.)                                                              0.280                                                                             0.272                                                                             0.361                                                                             0.358                                                                             0.241                                                                             0.254                                                                             0.297                                                                             0.312                                    tanδ (60° C.)                                                             0.145                                                                             0.153                                                                             0.187                                                                             0.225                                                                             0.132                                                                             0.138                                                                             0.172                                                                             0.173                                    __________________________________________________________________________     Remarks of Table I                                                            *.sup.1 Emulsified polymer SBR made by Nippon Zeon                            *.sup.2 Nipsil AQ: Silica made by Nippon Silica Kogyo                         *.sup.3 Diablack N339: Carbon black made by Mitsubishi Chemical               *.sup.4 see Reference Examples 1 and 2                                        *.sup.5 Silane coupling agent (Si69 made by Degussa)                          *.sup.6 Diethylene glycol                                                     *.sup.7 Noclac 6C (made by Ouchi Shinko Chemical Industries)                  *.sup.8 Nocceler D (made by Ouchi Shinko Chemical Industries)                 *.sup.9 Santocure NS (vulcanization accelerator made by Monsanto)        

INDUSTRIAL APPLICABILITY

As explained above, according to the present invention, it is possibleto provide a rubber composition having both a high wet grip and a lowrolling resistance as shown by a high tan δ at 0° C., as an indicator ofthe wet grip performance and a low tan δ at 60° C., as an indicator ofthe rolling resistance.

We claim:
 1. A rubber composition comprising a cross-linkable rubber anda surface-treated carbon black for rubber reinforcement, wherein saidsurface-treated carbon black is produced by heating carbon black andorganosiloxane together at a temperature of 60° C. to 200° C. to deposita silicon dioxide residue on the surface of the carbon black.
 2. Arubber composition according to claim 1, wherein the organosiloxanecomprises an alkyl group bonded directly to silicon, said alkyl groupcomprising 1 to 4 carbon atoms.
 3. A rubber composition according toclaim 2, wherein the organosiloxane comprises 3 to 1000 silicon atomsand an alkoxysilyl group.
 4. A rubber composition according to claim 3,wherein the amount of organosiloxane is 0.1 to 50% by weight, in termsof SiO₂, based upon the weight of the carbon black.
 5. A rubbercomposition according to claim 2, wherein the amount of organosiloxaneis 0.1 to 50% by weight, in terms of SiO₂, based upon the weight of thecarbon black.
 6. A rubber composition according to claim 1, wherein theorganosiloxane comprises 3 to 1000 silicon atoms and an alkoxysilylgroup.
 7. A rubber composition according to claim 1, wherein the amountof organosiloxane is 0.1 to 50% by weight, in terms of SiO₂, based uponthe weight of the carbon black.